No one would suggest leaving potentially dangerous, untested drugs on the market. But an outright ban hinders valuable research on compounds that could hold clues to treatments for diseases like Alzheimer’s.

As I wrote here last week, the Drug Enforcement Administration (DEA) had previously warned that it would place an emergency ban on five “legal high” substances commonly used in so-called fake marijuana.

As states race to outlaw synthetic drugs sold as “bath salts” or “fake marijuana,” there would seem to be little downside to banning these untested and possibly dangerous chemicals. But prohibiting “legal” intoxicants — many …